This invention generally pertains to control assemblies. More specifically, the present invention relates to a burner control assembly.
The invention is particularly applicable to a fuel control system for a burner which is used in a heat exchanger of a movable combustion heater that provides heated air to a confined space. However, it will be appreciated by those skilled in the art that the invention has broader applications and may also be useful in burners adapted for a wide variety of other applications outside the combustion heater field.
It is known to use movable air heaters for heating confined spaces such as shelters used by the military, trailers and a variety of portable buildings of various types. These heaters generally provide a fuel tank, a heat exchanger assembly, a fan and an engine, for pumping the fuel and driving the fan, on a trailer. However, such air heaters have not been completely satisfactory for heating confined spaces because they have been operated in an on/off manner in accordance with sensed air temperature. This type of heater operates at the maximum heating capacity and is alternately fired and shut off in response to a sensed air temperature that is, respectively, below and above a comfort zone in the space. A conventional heater of this type not only requires a relatively long warm up period but also results in the discharge of air at excessively high temperatures into the space after warm up.
It would be desirable to provide a heater with an automatic means for controlling the amount of fuel flow into a burner nozzle in a modulating fashion so as to obtain a selected discharge air temperature during the entire operation of the heater.
Another problem with conventional air heaters is that the air flow remains relatively constant due to the use of single speed fan driven by the engine even when the fuel flow is reduced because less heat is required. This leads to a large amount of excess air being supplied to the burner, which, in turn, leads to wide swings in the air/fuel ratio and hence poor combustion at lower fuel flows. Because so much extra air is introduced into the burner at low fuel flows, the combustion flame burns cool and produces excessive carbon monoxide levels and unburned hydrocarbons due to the excess air and low combustion temperature. Incomplete combustion also may result in the deposition of carbon on the inner walls and passages of the heat exchanger. Also, more fuel is required since all the excess air needs to be heated by the combustion process. A net savings of fuel could be obtained if the air flow to the burner could be limited along with the fuel flow since a hotter combustion flame would then be provided leading to a more efficient heat transfer process.
It would therefore be advantageous to provide an automatic means for controlling the amount of air flowing into a combustion chamber of a burner in relation to the amount of fuel flowing through a burner nozzle thereof in order to regulate the combustion process in the burner.
Accordingly, it has been considered desirable to develop a new and improved burner assembly which would overcome the foregoing difficulties and others and meet the above-stated needs while providing better and more advantageous overall results.